Method of making synthetic mica



limited States Patent Gfiice 3,01 1,8 68 Patented Dec. 5, 1961 This invention relates to a method of making synthetic mica and particularly to a method of making synthetic fluor-phlogopite mica.

In recent years practical methods of manufacturing synthetic mica have been developed. Basically, the methods employed for making synthetic mica are to introduce into a furnace shall raw batch materials of such composition that they provide the necessary molecular percentages for the final mica product, heating said ray materials until the raw materials melt, and thereafter cooling the materials to permit the mica to crystallize out of the liquid melt. Substantimly 106% of the final pig is mica. The preferred method of heating the batch materials is by internal resistance heating such as is dis closed in US. Patent No. 2,711,425, issued to R. A. Humphrey on June 21, 1955, for Electric rurnace and Electric Melting and Crystallizing Method for Minerals. The final a made by the Humphrey method or other si ilar methods is in the form of a huge chunk or pig which is diilicult to break up into usable plate-like crystals of mica. The chunk or pig of synthetic mica resulting from the Humphrey method is extremely tough and resists breaking up into the plate-like crystals which are commercially usable. Various methods of breaking up such a pig have been employed but most of them result in the breaking up of relatively large crystals into small crystals which have less commercial value. Moreover, in the Humphrey patent it is necessary to achieve tempcraturcs in the furnace equal to or above the melting temperature of the mica being made. These temperatures are extremely high. For instance, the melting point of fiuor-phlogopite mica is 1,365 C.

The present invention is a continuation of two earlier patent applications, Serial Nos. 681,431 and 681,432, filed by me September 3, B57, and now abandoned, for making synthetic mica in a novel way which is not subject to the disadvantages and limitations inherent in making synthetic mica in accordance with said Humphrey patent.

It is therefore one object of the present invention to provide a new and improved method for manufacturing synthetic mica.

Another object of the present invention is the provislo of a new and improved method for manufacturing synthetlc mica, wherein the crystal growth of the synthetic mica can be closely controlled.

Still another object of the present invention is the provision of a new and improved method for manufacturing synthetic mica, which method permits said manufacture at temperatures greatly below the melting point of the mica.

Yet another object of the present invention is to provide a method of crystallizing mica.

Another object of the present invention is to provide a method of crystallizing mica from a solvent therefor.

A further object of the present invention is to provide a method of recrystallizing mica.

Still a further obiect of the present invention is to provide a method of recrystallizing synthetic mica from a solvent therefor.

Yet a further object of the present invention is to provide a method of recrystallizing synthetic non-l1ydroxyl mica, such as iluor-phlogopite mica.

The above and other objects, characteristics and features of the present invention will be more fully understood from the following detailed desc iption.

Mica is a siliceous crystalline mineral which is commonly found in nature. Most of the mica found in nature includes water of constitution or hydroxyl (OH) ions.

An example of a hydroxyl mica is muscovite mica which has the formula KAl Si O (OH) The aforementioned Humphrey method is best adapted to make non-hydroxyl micas, that is, micas wherein ions other than hydroxyl replace or are substituted for the hydroxyl ions generally found in natural mica. The most common substitute for the hydroxyl ions are ions of the halogen group, preferably fluorine. Perhaps the most common mica made synthetically is normal fluor-phlogopite mica which has the chemical formula KMg Al-Si O F Other examples of non-hydroxyl micas are lithium tetra-silicic fiuor-phlogopite mica which is expressed by the formula KlVlg LiSi O F and barium di-silicic fiuor-phlogopite which is expressed by the formula BaMg Al Si O F Numerous other non-hydroxyl micas may be made. As is true with the Humphrey method, the present method is adapted for manufacturing synthetic non-hydroxyl micas such as, for instance, synthetic normal fluorphlogopite mice. The following detailed description of the method forming the present invention will be in connection with the manufacture of synthetic normal fluorphlogopite mica. However, it will be understood that the present method may also be employed to manufacture other synthetic non-hydroxyl micas such as, for instance, those mentioned above.

In the following description and in some of the claims annexed thereto, the term mica forming material will be employed. As used herein, the term mica forming material will mean mica and non-micaceous materials which are combinable to form mica.

I have recently discovered that non-hydroxyl mica forming material such as normal fluor-phlogopite mica or materials stoichiometrlcally equivalent tlereto are soluble in lead borate glass. Heretofore, no solvent for mica has been discovered from which the mica will pre cipitate out when the solution becomes saturated. With this discovery, a means and method for crystallizing and recrystallizing synthetic normal fluor-phlogopite mica is present.

In accordance with one aspect of the present invention, a batch of raw materials which have the stoichiometric content of mica and which are combinable to form mica are dissolved in heated lead bor-ate glass and after the batch materials have gone into solution, the lead borate glass may be cooled whereby to saturate the solution cause mica crystals to precipitate out of solution. Numerous combinations of batch materials may be employed for making any given mica. An example of a raw batch which has the various constituents of normal fiuor-phlogopite mica in proper stoichiometric proportions is presented below:

Percent Potassium silico fluoride (K SiF 19.77 Potash feldspar (KAlsi O 18.47 Silica (SiO 24.26 Alumina (A1 0 8.95 Magnesia (MgO) 28.55

Other combinations of raw materials forming a mica batch may readily be worked out by anyone skilled in the art. The lead borate glass which acts as a solvent for the mica batch mayhave a composition which falls within the following ranges:

Percent Lead oxide (PbO) 50 to 92 Boron, oxide (B 0 50 to 8 The method of the present invention is identical for a both mica forming materials. Thus, after the frit and the mica forming material have been well mixed by any suitable mechanical means or by hand mixing, the mixture is put into a container such as a platinum or ceramic crucible and heat is applied. The method of heating may be any suitable method but preferably, the crucible containing the mixture of mica forming material and frit is placed in an oven.

I have discovered that lead borate frit falling within the ranges disclosed above dissolves no mica batch when the frit temperature is below 450 C. However, at 800 C. the lead borate glass will dissolve about by weight of mica forming material, at 1,000 C. The lead borate glass will dissolve about 20% by weight of mica forming material, and at l,200 C. the lead borate glass will dissolve about 30% by weight of the mica forming material. At 1,365 C. as much mica as desired can be put into solution as normal fiuor-phlogopite mica is liquid at that temperature. I prefer to heat the mixture to about l,O50 C. at which temperature the lead borate glass solvent will dissolve about 22% by weight of the mica forming material since above 1,050 C. lead volatilizes out of the lead borate glass to thus create a substantial health hazard.

The mixture is held at the preferred temperature (800 C. to 1,200" C. and preferably 1,050 C.) preferably until all of the mica forming material is dissolved in the molten glass. The complete dissolution of the mica batch in the glass may be determined by removing a small amount of the molten material and rapidly quenching it, such as in water. Thereafter, a microscopic examination of the quenched material will reveal whether any raw material crystals are present. If no raw material crystals are present, then it may be presumed that all of the mica batch has been dissolved. On the other hand, the complete dissolution of the powdered synthetic mica in the glass may be determined by quenching and determining by microscopic examination Whether any mica crystals are present. Similarly, if no mica crystals are present then it may be presumed that all of the mica has been dissolved. However, if there are some raw material crystals or synthetic mica crystals still present, then the molten mixture is maintained at the desired temperature until the quench test indicates either total dissolution of the entire mica forming material, or that no more mica forming material can be dissolved.

After the mica forming material has been dissolved in the molten glass, the furnace may be shut off so as to permit a cooling of the entire molten mixture. As the solution cools, it, of course, is unable to hold in solution as much mica forming material as it was able to hold at the predetermined temperature. Accordingly, in one case the dissociated ions from the raw batch material combine to form mica crystals, which precipitate or crystallize out of themolten lead borate. In the other case, the dissociated ions from the ground up mica combine to form synthetic mica crystals which precipitate or recrystallize out of the molten lead borate glass. Since the mica crystals in both instances have a much lower specific gravity than the lead borate glass, they tend to rise to the top where they maybe scooped off.

The sizes of the mica crystals precipitating out of the solution may be controlled by controlling the rate of cooling, the slower the cooling the larger the crystals. If desired, the contents of the crucible may be cooled to some predetermined temperature such as, for instance, 800 C. to 950 C. and maintained at said temperature to permit the slow crystallization or recrystallization of the mica out of the solution and to further permit mica crystals to rise to the top of the relatively heavy lead borate glass. The holding temperature is dependent on the amount of mica forming material in solution and the amount of mica it is desired to get out of solution. The

h temperature at which the solution is held during the crystallizing or recrystallizing period should be such as to provide a lead borate glass which is sufiiciently viscous to prevent its flowing through the pores of the crucible but not so viscous as to retard the growth of the mica crystals.

I have further found that as the mica crystallizes or recrystallizes out of the lead borate glass, the lead borate glass tends to get less viscous. Accordingly, as another alternative embodiment of the present invention, instead of maintaining the lead borate glass solution at a constant temperature during the period of crystallization, the temperature of the solution may be gradually lowered whereby to maintain a constant viscosity of the liquid phase of the solution.

In lieu of mixing the ground frit with the powdered mica forming material before heating, the frit may be heated to the desired temperature and said mica forming material may be then introduced into the molten glass where it is dissolved as described above. In order to get a maximum amount of mica forming material into solution, it is desirable to stir the liquid while introducing the raw batch materials into already melted glass, that a more rapid dissolution of the mica batch material can be obtained by adding the oxides, i.e. SiO A1 0 and MgO, before adding the potassium silico fluoride and potash feldspar.

Regardless of whether or not the mica forming material is introduced before the lead borate glass is melted or after the melting of the lead borate glass, the present method can be made continuous by adding mica forming material to the molten liquid after mica crystals have been removed from the solution as by scooping them oif the top thereof and then raising the temperature of the liquid to dissolve the additional material. Accordingly, the entire method can be made to operate on a continuous basis and, in fact, it is possible to automatically control the entire process so that after the molten glass solution has been cooled to precipitate out mica, apparatus may be actuated to add mica forming material and then to raise the temperature of the solution and hold the solution at an elevated temperature until ail the mica forming material is dissolved, and thereafter, to lower the temperature of the solution to precipitate out additional mica crystals.

In lieu of scooping the mica crystals off the top of the lead borate solution as described above, the lead borate with the mica crystals dispersed therein may be slowly cooled to a temperature where it hardens. Thereafter, the lead borate glass may be dissolved in any suitable solvent such as a 5% solution of acetic or nitric acid, which solvent will not attack the mica. Accordingly, the lead borate glass will be removed by the solvent and the mica crystals will remain.

'llhe present method has a number of advantages over the methods herein before employed to make synthetic mica. Among these advantages are the fact that the rate of crystallization or recrystallization of the mica can be controlled by controlling the temperature of the solution and the viscosity thereof. Moreover, by controlling the rate of cooling, the size of the mica crystals can be controlled. Another important advantage of the present invention is that the manufacture of synthetic mica can take place at temperatures hundreds of degrees below the temperature heretofore necessary to manufacture synthetic mica. Another additional advantage of the present invention, as has been pointed out hereinbefore, is that the present method for making synthetic mica can be substantially continuous as contrasted with the batch methods heretofore employed.

Although the detailed description presented above was confined mainly to recr stall-izing synthetic normal fluorphlogopite mica, it will be understood that the above method will work for other non-'hydroxyl micas, such as other synthetic fluor-micas.

While I have herein shown and described several forms of the present invention and have suggested various changes and modifications therein, it will be understood that various other changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of this invention.

What I claim is:

1. A method of growing non-hydroxyl mica crystals, comprising the steps of dissolving non-hydroxyl mica forming material in heated lead borate glass and then cooling the resulting solution to cause said mica to precipitate out of solution.

2. A method of making synthetic non-hydroxyl mica,

comprising the steps of dissolving non-:hydroxyl mica forming material in lead borate glass heated to a temperature between about 450 C. and 1365 C. and then cooling the resulting solution to cause said mica to precipitate out of solution. 3. A method of making synthetic non -hydroxyl mica, comprising the steps of dissolving non-hydroxyl mica forming material in lead borate glass consisting essentially of 50% to 92% lead oxide and 50% to 8% boron trioxide heated to a temperature between about 450 C. and 1365 C. and then cooling the resulting solution to cause said mica to precipitate out of solution.

4. A method of making synthetic non-hydroxyl mica, comprising the steps of dissolving raw materials which contain constituents chemically com-binable to form said mica in heated lead borate glass, and (then cooling the resulting solution to cause said mica to precipitate out of solution.

5. A method of making synthetic floor-mica, comprising the steps of dissolving raw materials which contain constituents chemically combinable to form said mica in heated lead borate glass, and then cooling the resulting solution to cause said mica to precipitate out of solution.

6. A method of making synthetic fluor-phlogopite mica, comprising the steps of dissolving raw materials which contain constituents chemically combinable to form said mica in heated lead borate glass, and then cooling the resulting solution to cause said mica to precipitate out of solution.

7. A method of making synthetic normal fluor-phlogopite mica, comprising the steps of dissolving raw materials which contain constituents chemically combinable to form said mica in heated lead borate glass, and then cooling the resulting solution to cause said mica to precipitate out of solution.

8. A method of making synthetic normal fluor-phlogopi-te mica, comprising the steps of dissolving raw materials which contain constituents chemically combinable to 'fonm said mica in heated lead borate glass, and then cooling the resulting solution to cause said mica to precipitate out of solution, said lead borate glass consisting essentially of from 50% to 92% lead oxide and 50% to 8% boron oxide. 7

9. A method of making synthetic normal fluor-phlogopite mica, comprising the steps of dissolving raw materials which contain constituents chemically combinable to form said mica in lead borate glass'heated to above 450 C., and then cooling the resulting-solution to cause said mica to precipitate out of solution.

10. A method of making synthetic normal fluor-phlogopite mica, comprising the steps of dissolving raw materials which contain constituents chemically combinable to form said mica in lead borate glass heated to between 800 C. and 1,200 C. and then cooling the resulting solution to cause said mica to precipitate out of solution.

11. A method of making synthetic normal fluor-phlogopite mica, comprising the steps of heating lead borate glass consisting essentially of about 50% to 92% lead oxide and about 50% to 8% boron oxide to between about 800 C. and 1,200 C., dissolving raw materials which contain constituents chemically combinable to form said mica in said lead borate glass, and then cooling the resulting solution to cause said mica to precipitate out of solution.

12. A method of making synthetic fluor-phlogopite mica, comprising the steps of heating lead borate glass consisting essentially of about 50% to 92% lead oxide and about 50% to 8% boron oxide to between about 800 C. and 1,200 C., dissolving raw materials which contain constituents chemically conrbinable to :form said mica in said lead borate glass, and then cooling the resulting solution to cause said mica to precipitate out of solution.

13. A method of making synthetic normal fluor-phlogopite mica, comprising the steps of heating lead borate glass to between about 800 C. and 1,200 C., adding raw batch material consisting essentially of about 19.77% potassium silico fluoride, 18.47% potash feldspar, 24.26% silica, 8.95% alumina and 28.55 magnesia to said lead borate, dissolving at least some of said batch material in said heated lead borate glass, and then cooling said solution to cause normal fluor-phlogopite mica to precipitate out of said solution.

14. A method of making synthetic normal fluor-ph-logopite mica, comprising the steps of heating lead borate glass consisting essentially of about 50% to 92% lead oxide and 50% to 8% boron oxide to between about 800 C. and 1,200 C., adding raw batch material consisting essentially of about 19.77% potassium silico fluoride, 18.47% potash feldspar, 24.26% silica, 8.95% alumina and 28.55% magnesia to said lead borate glass, dissolving at least some of said batch material in said heated lead borate glass, and then cooling said solution to cause normal fluor-phlogopite mica to precipitate out of said solution.

15. A method of making synthetic normal fluorphlogopite mica, comprising the steps of heating lead borate glass consisting essentially of about 81.4% lead oxide and 18.6% boron oxide to between about 800 C. and 1,200 C., adding raw batch material consisting essentially of about 19.77% potassium silico fluoride, 18.47% potash feldspar, 24.26% silica, 8.95% alumina and 28.55% magnesia to said lead borate, dissolving at least some of said batch material in said heated lead borate glass, and then cooling said solution to cause normal fluor-phlogopite mica to precipitate out of said solution.

16. A method of making synthetic normal fluorphlogopite mica, comprising the steps of heating lead borate glass consisting essentially of about 81.5% lead oxide and 18.6% boron oxide to about 1,050 C., adding raw batch material consisting essentially of about 19.77% potassium silico fluoride, 18.47% potash feldspar, 24.26% silica, 8.95% alumina and 28.55 magnesia to said lead borate glass, dissolving at least some of said batch material in said heated lead borate glass, and then cooling said solution to cause normal fiuor-phlogopite mica to preci- I cause normal fiuor-phlogopite mica to precipitate out of said solution.

18. A method of making synthetic normal fluorphlogopite mica, comprising the steps of heating lead borate glass consisting essentially of about 81.5% lead oxide and 18.6% boron oxide to about 1,050 C., taking raw batch material consisting essentially of about 19.77% potassium silico fluoride, 18.47% potash feldspar, 24.26% silica, 8.95% alumina and 28.55% magnesia, first adding to and dissolving in said heated lead borate glass the silica, alumina and magnesia, then adding to and dissolving in said heated lead borate glass the potassium silico fluoride and potash feldspar, and then cooling said solution to cause normal fluor-phlogopite mica to precipitate out of said solution.

19. A method of making synthetic non-hydroxyl mica,

comprising the steps of dissolving batch materials consisting of constituents which chemically react to form said mica in heated lead borate glass, and then cooling said solution to cause said mica to precipitate out of solution.

, 20. A method of making synthetic non-hydroxyl mica, comprising the steps of substantially totally dissolving raw materials containing constituents chemically combinable to form said mica in heated lead borate glass, and then cooling said solution to cause said mica to precipitate out of said solution.

21. A method of recrystallizing non-hydroxyl mica, comprising the steps of heating lead borate glass to a temperature between about 450 C. and 1365 C., dissolving mica in said heated lead borate glass, and then cooling said solution to cause mica to precipitate out of said solution.

22. A method of recrystallizing fluor-mica comprising the steps of heating lead borate glass to a temperature between about 450 C. and 1365 C., dissolving fiuor-mica in said heated lead borate glass, and then cooling said solution to cause fluor-mica to precipitate out of said solution.

23. A method of recrystallizing synthetic fluorphlogopite mica, comprising the steps of heating lead borate glass consisting essentially of from about 50% to 92% PbO and from about 50% to 8% B to a temperature between about 450 C. and 1365 C., dissolving synthetic fluor-phlogopite mica in said heated lead borate glass, and then cooling said solution to cause said mica to precipitate out of said solution.

24. A method of recrystallizing synthetic fluorphlogopite mica, comprising the steps of heating lead borateglass consisting essentially of about 81.6% FM) and about 18.4% B 0 to a temperature between about and 1365 C., dissolving synthetic fluorphlogopite mica'in said heated lead borate glass, and then cooling said solution to cause said mica to precipitate out of said solution.

25. A method of recrystallizing synthetic fluorphlogopite mica, comprising the steps of heating lead borate glass consisting essentially of from about 50% to 92% PhD and from about 50% to 8% B 0 to a tem- 'perature between about 800 C. and 1,200 C., dissolving synthetic fluor-phlogopite mica in said heated lead P130 and from about 50% to 8% B 0 to a temperature of about'1,0'50 C., dissolving synthetic fiuor-phlogopite mica in said heated lead borate. glass, and then cooling solution.

saidsolution to cause said micaito precipitate out of said 27. A method of recrystallizing synthetic fiuor-phlogopite mica, comprising the steps of heating lead bora-te glass consisting essentially of about 81.6% PbO and about 18.4% B 0 to a temperature between about 800 C. and 1,200 C., dissolving synthetic fiuo'r-phlogopite mica in said heated lead borate glass, and then cooling said solution to cause said mica to precipitate out of said solution.

28. A method of recnystallizing synthetic fluor-phlogopite mica, comprising the steps of heating lead boi'ate glass consisting essentially of about 81.6% P130 and about 18.4% B 0 to a temperature of about 1,050 C., dissolving synthetic floor-phlogopite mica in said heated lead bora-te glass, and then cooling said solution to cause said mica to precipitate out of said solution.

29. A method of recrystallizing synthetic fluor-phlogopite mica, comprising the steps of mixing powdered synthetic fiuor-phlogopite mica together with powdered lead borate firit, heating said mixture to a temperature between about 450 C. and' 1365 C. .to cause at least a part of said mica to dissolve in said lead bor-ate, and then cooling said solution to cause said mica to precipitate out of said solution.

30. A method of recrystallizing non-hydroxyl mica, comprising the steps of heating lead borate glass consisting essentially of from about 50% to 92% PbOand from about 50% to 8% B 0 to a temperature between about 450 C. and 1,365 C., dissolving non-hydroxyl mic-a in said heated lead borate glass, and then cooling said solution to cause said mica to precipitate out of said solution.

31. A method of recrystallizing'fiuor-mica, comprising the steps of heating lead borate glass consisting essentially of fi'orn about 50% to 92% P and from about 50% to 8% B 0 toa temperature between about 450 C. and 1365 C., dissolving floor-mica; in said heated lead borate glass, and then cooling said solution to cause said mica to precipitate out of said solution.

32. A method of recrystallizing synthetic normal fluorphlogopite mica, compressing the steps of heating lead borate glass consisting essentially of from about 50% to 92% PhD and from about 50% to 8% E 0 toa temperature between about 450 C. and 1365 C., dissolving synthetic normal fiuor-phlogopite mica in said heated lead borate glass, and then cooling said solution to cause said mica to precipiatte out of said solution.

33. A method of recrystallizing non-hydroxyl mica, comprising the steps of dissolving said mica in lead ho-rate glass, and then cooling said solution to cause at least a portion of said disoslved mica to precipitate from said solution. I a

34. A method of growing normal fiuor-phlogopite mica crystals, comprising the steps of heating lead borate glass consisting essentially of about 50% 40.92% lead oxide and about 50% to 8% boron oxide to between about 800 C. and 1200 C., dissolving normal fluor-phlogopite mica forming material in said lead borate glass, and then cooling the resulting solution to cause said mica to precipitate out of solution.

References Cited in the tile of this patent Australia May 10, 1950 

3. A METHOD OF MAKING SYNTHETIC NON-HYDROXYL MICA, COMPRISING THE STEPS OF DISSOLVING NON-HYDROXYL MICA FORMING MATERIAL IN LEAD BORATE GLASS CONSISTING ESSENTIALLY OF 50% TO 92% LEAD OXIDE AND 50% TO 8% BORON TRIOXIDE HEATED TO A TEMPERATURE BETWEEN ABOUT 450*C. AND 1365* C. AND THEN COOLING THE RESULTING SOLUTION TO CAUSE SAID MICA TO PRECIPITATE OUT OF SOLUTION. 